About 25 people died when a fishing boat carrying hundreds of migrants capsized on Wednesday in the Mediterranean Sea, about 15 miles north of the Libyan coast, the Italian coast guard said, as rescue operations were still under way.

About 400 people were rescued so far in operations coordinated by the Italian coast guard, spokesman Filippo Marini told Italian television, adding that the distressed boat may have been carrying as many as 600 migrants.

Another coast-guard spokesman said up to seven ships were involved in the rescue, including an Irish naval vessel and a boat operated by Doctors Without Borders, which were the first two to intervene. According to preliminary reports, the fishing boat capsized after the migrants moved to one side once they saw two rescue boats approaching, the spokesman said.

Wednesday’s deadly shipwreck is just the latest development in a growing wave of migrants who cross the Mediterranean to reach Europe, often seeking to escape war and persecution. Italy and Greece have seen a surge in the number of migrants reaching its shores: About 97,000 people have tried to reach Italy so far this year, with another 90,500 landing in Greece. According to the International Organization for Migration’s latest data, more than 2,000 people have died so far this year trying to cross the Mediterranean, the vast majority of whom were seeking to land in Italy.

As in 2014, the overwhelming majority died in the Strait of Sicily in the central Mediterranean route connecting Libya and Italy, where unseaworthy vessels used by smugglers and traffickers significantly increase the likelihood of tragedies, the IOM said.

In April, about 800 migrants died when a ship sunk off the Libyan coast in one of the deadliest incidents ever recorded. With the Syrian civil war escalating and more refugees desperately trying to leave war zones as well as an increasingly unstable situation in Libya, the number of migrants trying to flee their countries of origin has been on the rise.